This invention relates to novel composites comprising aluminum oxide and/or solid solutions and/or multiphase compositions of aluminum oxide with one or more other metal oxides, a reactive metal oxide phase and/or solid solutions containing said oxide, and a metallic phase and relates to apparatus formed therefrom such as cutting tools and wear and abrasion and oxidation resistant surfaces.
It is known that aluminum oxide has the characteristic of excellent wear resistance. The material is used as cutting tools for metals and for wear resistant surfaces. It is believed that the primary reasons for this characteristic are that aluminum oxide is a hard material which minimizes abrasive wear and because it has a very negative .DELTA.G of formation which minimizes its thermally activated chemical dissociation and reaction with the workpiece. Aluminum oxide has been used in the form of coatings on conventional carbide tools, said coatings formed by processes such as vapor deposition or sputtering, but the coating is weakly adhered to the substrate which results in the coating being flaked off the substrate. It is known also that the mechanical properties of aluminum oxide can be improved by forming solid solutions with other oxides such as chromium oxide, or by forming multiphase compositions with other oxides such as zirconium oxide. Furthermore, it is known also to form aluminum oxide cutting tools by a sintering or a hot pressing process to form fine grained aluminum oxide which may also include grain boundary pinning additives such as magnesium oxide or tungsten. However, the resultant tools are too brittle for most steel cutting operations and their use is limited to finishing cuts because of their inability to withstand even medium chip loads or vibration between the tool and workpiece without fracture. Attempts have been made to fabricate aluminum oxide based cermets for cutting tools with little success due to the inability to bond aluminum oxide to metals and thereby increase the fracture toughness of the resulting composite.
It would be desirable to provide composites comprising aluminum oxide and/or solid solutions and/or multiphase compositions of aluminum oxide with one or more other metal oxides bonded to a metallic phase, the resultant composite having improved fracture toughness as compared to the aluminum oxide cutting compositions of the prior art. Such compositions would be capable of utilizing the desirable cutting characteristics of aluminum oxide under more severe cutting conditions than is now presently possible.